1. Field of the Invention
The present invention relates to a phosphor for a cathode-ray tube, which has good coating characteristics with respect to a cathode-ray tube, and a surface treatment method for the phosphor.
2. Description of the Related Art
In general, a phosphor screen of a color cathode-ray tube is formed by coating a phosphor slurry in the form of dots or stripes on a face plate by photographic printing. This phosphor slurry is prepared by dispersing phosphor particles in a photosensitive resin solution containing ammonium dichromate, PVA (polyvinyl alcohol), and a surfactant.
A phosphor screen thus formed is required to have, primarily, the following coating characteristics:
1. Dense dots or stripes are formed with a uniform thickness.
2. The shape of dots or stripes is precise. That is, all phosphor dots or stripes of respective colors are formed at predetermined positions with a predetermined shape, a predetermined width, and a predetermined size.
3. Dots or stripes do not peel from a face plate.
4. No color mixing is caused between phosphor particles. That is, luminescent components constituted by red, blue, or green phosphor particles coated in the form of dots or stripes do not overlap adjacent luminescent components of different colors; i.e., no color mixing is present.
5. No haze is caused. That is, after dots or stripes constituting luminescent components are formed, no extra portion to be washed away remains on a face plate.
The above coating characteristics are affected by the surface condition of phosphor particles. For this reason, phosphor particles containing various surface treatment substances adhered or attached on their surfaces have been conventionally developed.
One of surface treatment substances to be adhered on phosphor particles and easiest to use is SiO.sub.2. A phosphor containing SiO.sub.2 as the surface treatment substance is manufactured by adding a silicate compound to a phosphor suspension, and adding an aqueous solution containing, e.g., Zn, Al, Mg, Ba, or Ca to the resultant solution, thereby producing a silicon compound on the surface.
Published Examined Japanese Patent Application No. 50-15747 discloses a method of performing a surface treatment for a phosphor by adding water glass and zinc sulfate to an aqueous suspension of the phosphor.
Published Examined Japanese Patent Application No. 61-46512 discloses a phosphor on which silica, a zinc compound, and an aluminum compound is adhered.
The phosphors described in the above patent applications, however, are still unsatisfactory to satisfy all of the characteristics of items 1 to 5 above.
For example, when zinc silicate is caused to be adhered on phosphor particles, dispersibility of the phosphor in the photosensitive resin solution described above is improved, and consequently the characteristics of items 1, 2, and 3 above are satisfied. However, since phosphor particles are scattered to adjacent dots, the characteristics of items 4 and 5 above cannot be satisfied.
The phosphor which is surface-treated with water glass and zinc sulfate cannot sufficiently satisfy any of the characteristics of items 1 to 5 above.